Method of preparing mixtures of carbon monoxide and hydrogen



Jan. 2, 1940.

G. ROBERTS, JR

IETHOD 0F PREPARING IIXTURES OF CARBON HONOX IDE AND HYDROGEN Filed Aug., 19, 1938 Illlllll Tlivll'lllllllllllll... II.- llllllllllll llllllll INVENTOR 6w f'gefiober I'llllllllllllllllll llllllkil TORNEY Patented 1940 UNITED STATES METHOD OF PREPARING MIXTURES OF- CARBON MONOXIDE AND HYDROGEN George Roberts, In, Montclair, N. 1., assignor to The M. W. Kellogg Company, New York, N. Y a corporation of Delaware Application s me 18, ms, sol-m No. 225.155 6 claim. (01. 23-212) My invention relates to a method of preparing raw material gases in predetermined proportions for the production of a mixture of carbon monoxide and hydrogen, or more particularly, synthesis gas for use in various catalytic synthesis processes.

It is well known that synthesis gas (mixtures of carbon monoxide and hydrogen) may be formed from methane, carbon'dioxide and steam,

at temperatures between 1800 F. and 2200 F. in the presence of a catalyst.

Methane will combine with carbon dioxide and The above method being known, does not of itself comprise my invention, which resides in the novel combination which will be hereinafter more fully pointed out. a It has been suggested that carbon dioxide may be recovered from flue gas or previously reacted synthesis'gas, or any gas rich in carbon dioxide. such as fermentation gas, or the like. The carbon dioxide containing gas is introduced into an absorption tower where it is contacted with 25 monoethanolamine, diethanolamine, or other menstruum which has an afflnity for carbon dioxide. In the case of flue gas as 'a source of carbon dioxide, the unabsorbed gas usually contains nitrogen, which passes off from the top or the absorption tower. The carbon dioxide absorbed in the menstruum is passed to a stripper and stripped of its carbon dioxide by means of steam. The use of steam makes the process of recovery of carbon dioxide very expensive in some cases, 35 and the result is that in many cases the recovery of carbon dioxide from flue gases or the like might be uneconomical.

One objectof my invention is to provide an .economical method of generating synthesis gas 40 A further object of my invention is to provide a method of generating synthesis gas in which the methane used in whole or in part for the synthesis gas generation is employed as a stripping medium to strip absorbed carbon dioxide from the liquid menstruum.

Other and further objects of my invention will appear from the following description.

The accompanying drawing, which forms part of the instant specification andwhich is to be read 50 in conjunction therewith, is a diagrammatic view of one form of apparatus capable of carrying out the method of my invention.

More particularly, referring now to the drawings, methane or natural gas from any suitable 3 source is introduced into absorber I through pipe 2, controlled by valve 3. A sulfur absorbing menstruum, such as triethanolamine, is introduced into the absorber tower I through pipe 4, flows downwardly in contact with the rising inethanef Hydrogen sulfide and other sulphur compounds are absorbed by the menstruum and are withdrawn from theabsorber I through pipe 5, and pumped by pump 6 through pipe I through heat exchanger 8, through pipe 9, and introduced into a still ill. The menstruum is reboiled by reboiler ll through heat ,irom steam introduced to the reboiler through pipe l2. Hydrogen sulflde and light suliur bearing compounds are distilled from the menstruum and pass overhead through pipe l8 through condenser H, which is furnished a cooling medium through pipe ii.

The condensate and uncondensed hydrogen sulflde are withdrawn from the condenser through pipe l8 and passed to a separator H, from which the hydrogen sulfide is withdrawn through pipe l8, controlled by back pressure controlled valve It. Any of the menstruum which has been vaporized is recovered as a condensate and withdrawn from the separator through pipe 28 and pumped by pump 2| through pipe 22 to the top of the still as a top tower temperature control reflux. The denuded menstruum is withdrawn from the bottom of the still through pipe 23 and pumped by pump 24 through pipe 25, through heat exchanger 8, through pipe 26, through cooler 21, and thence through pipe 4 for introduction into the absorber. The cooler is supplied a cooling medium through pipe 28. The methane or natural gas denuded of sulfur compounds is withdrawn from the absorber through pipe 29, and is led by pipe 30 to the bottom of stripping tower 58. A-portion of the methane may pass through pipe 32, controlled by valve 33, into pipe 84, which passes to the synthesis gas generating zone, indicated diagrammatically by the reference numeral 35.

Any suitable carbon dioxide bearing gas, such as flue gas, waste gas from the synthesizing step in which the, synthesis gas is used, fermentation gases, or the like, is introduced into .the absorber 4| through pipe 42, controlled by valve 43. A menstruum having an aflinity for carbon dioxide, such as-monoethanolamine, diethanolamine, and the like, is introduced into the absorber through pipe 44. The menstruum with absorbed carbon dioxide is withdrawn from the bottom of the absorber through pipe 45 and pumped by pump f' ing tower Ill.

The temperature at the bottom of the stripper is maintained at a predetermined point by means of reboiler ii, to which steam is supplied through pipe 52. Methane being introduced into the stripper through pipe strips the carbon dioxide from the absorbed menstruum. Due to the stripping effect of methane, very little steam need be used through pipe 52. Furthermore, with the use of methane the temperature at the top of the stripper may be maintained at such a point that water vapor will leave the top of the stripper tower through pipe 53 along with the stripped carbon dioxide and methane. This allows a greater temperature difference to be employed in the top reflux condenser 54, and thereby reduces the surface required. The water balance must be made in the CO2 recovery system. If more water is leaving as vapor than enters as vapor, make-up water may be added at any suitable place as, for example, through pipe 3! into the absorber. The condensate, uncondensed gases or vapors, and incondensable gases, such ascarbon dioxide and methane, leave the condenser through pipe 56 and pass into a separator 51, from which methane, carbon dioxide and a por tion of water vapor are withdrawn through pipe 58, controlled by back pressure controlled valve 58.

Any of the absorption menstruurn which passes overhead as vapor, and a certain proportion of water will form the condensate which is removed from the separator 51 through pipe 60 and pumped by pump GI through pipe 82 into the stripper 50. The denuded menstruum is removed from the stripper through pipe 63 andpumped by pump 64 through pipe, through heat exchanger 48 through pipe 66, through cooler 61, through pipe 44, for introduction into the absorber tower. Cooling medium is supplied the cooler 61 through pipe 68. The waste gases denudedo'f carbon dioxide are removed from the absorber through pipe 69, controlled by valve 10. The gases withdrawn from the separator 51 through pipe 59' will contain carbon dioxide (recovered), methane (the stripping medium), and a small portion of water vapor.

The desired proportion of water in the mixture going to the synthesis gas generator is controlled by introducing steam through pipe I I, controlled by valve 12. The mixture of carbon dioxide, methane and steam then passes through pipe 13 into pipe 34, whence it flows to the synthesis gas generator 35. The correct ratio of methane is maintained by adding additional methane through pipe 32, controlled by valve 33.

It will be seen that I have accomplished the objects of my invention. I have provided a convenient and expeditious method of forming synthesis. gas in which carbon dioxide is recovered by an absorption menstruum and strippedby a light desulfurized gas such as methane, which is itself usedin forming the synthesis gas so that no separation need be made betweenthe stripping gas and the stripped gas. The practice enables the saving of process steam, which in ture diflerence on the top reflux'cooler, thereby aromas reducing the surface required. The water vapor,

it will be noted, forms a portion of the reacting gases which pass to the synthesis gas generator.

The method described is of particular utility in. those cases where the carbon dioxide absorbent has a very low vapor pressure. On the other hand, when an absorbent having a high vapor pressure is used, a part of it would be vaporized by the methane and would be carried thereby to the synthesis gas production step. 7

While the production of a mixture of methane, carbon dioxide and steam is particularly adapted for the manufacture of carbon monoxide and hydrogen to be used in synthesis, the mixture may also be used for other purposes than the production of synthesis gas. the combination of methane, carbon dioxide and steam mixed in the manner set forth may be used in the production of chemicals, or for innumerable purposes besides synthesis, and the invention contemplates such uses, as well as the synthesis gas production described.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and sub-combinations. This is contemplated by and is within the scope of my claims. It is further obvious that various changes may be made in details within the scope of my claims without departing from the spirit of my invention. It is, therefore, to be understood that my invention is not to be limited to the specific details shown and described.

Having thus described my invention, I claim:

1. A: method of preparing a mixture of carbon monoxide and hydrogen for catalytic synthesis including the steps of desulfurizing methane to remove objectionable sulfur compounds, subjecting a carbon dioxide-bearing gas to absorption by an absorption menstruum se- 2. A method as in claim 1 in which steam is added to the mixture of carbon dioxide and methane before its passage to the synthesis gas generating zone.

3. A method of preparing a mixture of-carbon monoxide and hydrogen for catalytic synthesis including the steps, of subjecting a carbon dioxide-bearing gas to absorption by an absorption menstruum selective to carbon dioxide in an absorption zone to form an enriched menstruum, stripping the carbon dioxide from the enriched menstruum by means of methane, passing the stripped carbon dioxide and methane to a synthesis gas generating zone and there subjecting them to a temperature above 1500 F. in the presence of a cataylst.

4. A method of preparing a mixture of carbon monoxide and hydrogen for catalytic syn thesis including the steps of subjecting a carbon dioxide bearing gas to. absorption by an absorption menstruum selective to carbon dioxide in an absorption zone-to form an enriched menstruum, stripping the carbon dioxide from the enriched menstruum by means of methane, passing the In other words, a

thesis including the steps of subjecting a carbon dioxide bearing gas to absorption by an absorption menstruumselective to carbon dioxide in an absorption zone to form an enriched menstruum, stripping the carbon dioxide from the enriched menstruum by means of methane, controlling the temperaturein the stripping stage to avoid loss or the absorbing menstruum through vaporization, passing the stripped carbon dioxide and-methane vto-a synthesisgas generating zone and there subiectingthem tea-temperaturev 5 above 1500 F.- in the presence of a. catalyst.

6. .A method ,as in claim 5 wherein ther-carbon dioxide stripping step is carried on in the presence of introduced water and the temperature in said stripping step is maintained at a 10 point to permit the vaporization of water.

, GEORGE ROBERTS, JR. 

